Fabrication and performance of SiO2–based electromagnetic wave penetrating foamed ceramics with dense surface

Abstract SiO2–based foamed ceramics with good comprehensive performance of electromagnetic wave penetration, thermal insulation and water resistance were fabricated from a powder mixture including quartz, calcium carbonate, talc and Si3N4 by a direct foaming method. The sintering temperature and the Si3N4 content in the mixture are two key factors affecting the microstructure, phase composition and performance of the foamed ceramics. Owing to its porous internal structure with high total porosity of 89% and dense surface with few small pores, the foamed ceramic fabricated by sintering at 1200 °C from the mixture containing 18 wt% Si3N4, which shows a bulk density, permittivity and permeability as low as 0.31 g/cm3, 2.16+j0.007 and 1+j0 respectively, closed porosity as high as 87%, and relatively high compressive strength of 6.1 MPa, is an excellent electromagnetic wave penetrating material possessing good performance of thermal insulation and water resistance.